For this purpose, CAL diodes (CAL=Controlled Axial Lifetime) and EMCON diodes (EMCON=Emitter Controlled) have become established in the past. In the case of CAL diodes, a heavily doped p-type emitter is used, but the latter additionally requires intensive helium irradiation and further methods for reducing the charge carrier lifetime in order that the turn-off losses do not become too high. EMCON diodes, by contrast, have a relatively weakly p-doped emitter. However, a reduced surge current strength is disadvantageous in this case.
A further diode variant is the so-called “speed diode”. FIG. 1a shows a detail from such a speed diode in a vertical section. The speed diode comprises a semiconductor body 1 with an edge 13. In the semiconductor body 1, a heavily n-doped zone 8, a weakly n-doped zone 7 and a p-doped zone 6 are arranged successively in a vertical direction v. A pn junction 4 is formed between the weakly n-doped zone 7 and the p-doped zone 6, and constitutes the load junction 4 of the speed diode. The p-doped zone 6 is part of the so-called p-type emitter, and the heavily n-doped zone 8 is also referred to as an n-type emitter.
Arranged in the p-doped zone 6 are a number of identical heavily p-doped islands 51-57 which are arranged in a manner spaced apart equidistantly with respect to one another and extend into the p-doped zone 6 proceeding from the front side 11 of the semiconductor body 1. While the forward current of the diode essentially flows via the weakly p-doped zone 6 during normal operation, in the surge current case charge carriers are injected from the heavily p-doped islands 51-57 into the weakly p-doped zone 6.
The speed diode furthermore has an edge structure 60 formed as a p-type field ring. FIG. 1b shows a horizontal section in a plane El running through the heavily p-doped islands 51-57. The vertical section in accordance with FIG. 1a runs in a plane E2 parallel to the vertical direction v. It can be seen from the illustration in accordance with FIG. 1b that adjacent heavily p-doped islands 51-57 are spaced apart equidistantly with respect to one another both in a first lateral direction r1 perpendicular to the vertical direction v and in a second lateral direction r2 perpendicular to the vertical direction v and to the first lateral direction r1.
In the case of this speed diode, however, relatively high overall losses occur on account of a high charge carrier density in the edge region of the pn load junction 4. Furthermore, its dynamic robustness is unsatisfactory.